This invention relates to a variable reluctance type rotation angle detection device capable of detecting not only rotation angle but also a rotation speed and rotation acceleration together by using a common detection head unit and, more particularly, to a detection device comprising a variable reluctance type detection head unit producing an output signal by phase shifting or phase modulating a reference AC signal in accordance with a present position of rotation.
Known in the art of rotation angle detectors are a potentiometer, a resolver, a rotary differential transformer, an optical rotary encoder and the like device. A potentiometer is short in life for it is a contact type device. A resolver which needs a brush has problems in durability, high speed response and noise. Although there exists a resolver which has obviated a brush by providing a rotary transformer, provision of such rotary transformer has the disadvantage that the device requires a complicated and large device. A rotary differential transformer which obtains an analog output corresponding to a sine wave amplitude corresponding to a rotation angle is incapable of producing a linear output over all of the rotation range. A common disadvantage in the rotary differential transformer and the potentiometer is that these devices tend to cause errors due to disturbance, for they produce a voltage level corresponding to a rotation angle. For example, in these devices, variation in resistance of a coil due to change in the temperature causes variation in the level of the detection signal. Reliability in these devices is inadequate because attenuation of the level in signal transmission paths from the detector to a circuit utilizing the detection signal differs depending upon the distance of the transmission paths. Further, variation in the level due to noise is directly outputted as a detection error. For the various reasons stated above, it is difficult to construct an absolute encoder of a high resolution by the prior art electromagnetic type rotation angle detector. On the other hand, the optical type encoder which has a function of an absolute encoder is disadvantageous in that its resolution of detection is lifted by an area of a pattern disk so that an increase in resolution necessitates an increase in the area of the pattern disk with a result that a large pattern disk and, accordingly, a large detector is required. The optical type encoder is also disadvantageous in that it is generally expensive, that the whole pattern disk must be replaced if change in resolution or a code type of data is required and that the pattern disk tends to get broken if it is made of a glass plate so that an environment in which it can be used is limited.
Prior art rotation speed meters are generally classified into those which produce an analog voltage (or current) proportionate to the rotation speed (i.e., revolution number per unit time) and those which produce a pulse train proportionate to the rotation speed. Common disadvantages in the devices producing an analog output are that, as described above, they tend to cause errors due to disturbance and that increase in resolution is limited. The devices producing a pulse train are also limited in resolution and rangebility (range of detectable revolution number), for the number of pulse produced per one rotation is limited due to the mechanism of the device. Besides, there has been no rotation acceleration meter having a wide detection range and a high resolution.